In an appearance Wednesday before the Senate Judiciary Committee, Holder said that the government also will hunt down any people and groups that exploit the stolen data through credit card fraud.

Hackers stole about 40 million debit and credit card numbers in the pre-Christmas data heist. They also took personal information - including email addresses, phone numbers, names and home addresses -- of another 70 million people.

Minneapolis-based Target says it is working with the Secret Service and the Justice Department in response to the data breach.